1. Field of the Invention
This invention relates generally to improvements in gas turbine engines and, more particularly, to rotating seals used in such engines.
2. Description of the Prior Art
Rotary seals of the labyrinth-type, comprising one or more circumferential teeth, one part which are contiguous with a circumferential sealing surface on another part, the two parts or elements being relatively rotatable, are commonly used in gas turbine engines to assist in direction of engine service air flows. Seals of this type are used to restrict air flow within cavities formed between stationary and rotating members of the engine without impeding the rotational movement of the rotating member. In addition, rotating seals have been used to assist in balancing the main engine bearing axial thrust loads.
A disadvantage of seals of this type is that they are formed of relatively complex hardware components which are expensive to machine and difficult to assemble. In addition, some of the parts of the seal assembly protrude into adjoining stationary cavities. The rapid revolution of the rotating seal with respect to the air within the stationary cavity causes that air to heat due to the windage friction engendered by the protruding parts. Further, due to their relatively complex structure, prior art rotating seals have a relatively large minimum radial dimension or length which is subject to thermal stresses due to the radial thermal gradient present in gas turbine engines. This relatively large minimum radial dimension further limits the flexibility for using a rotating seal to assist in balancing the main engine bearing axial thrust loads since the designer is limited to a certain minimum area of the rotating seal disc.
Accordingly, one object of the present invention is to provide a rotating seal having a minimal number of components which are relatively inexpensive to machine and easy to assemble.
Another object of the present invention is to provide a rotating seal which causes minimum temperature rise in the surrounding air due to windage friction.
A further object of the present invention is to provide a rotating seal having an active air circuit which reduces thermal stresses due to thermal gradients.
Yet another object of the present invention is to provide a rotating seal having an active air circuit which reduces the thermal time constant of the seal disc bore which in turn reduces the thermal gradient between the disc bore and the seal rim during gas turbine engine transient operation.